The invention is generally related to the field of forming high dielectric constant (high-xcexa) films in semiconductor devices and more specifically to forming high-xcexa gate dielectrics.
As semiconductor devices have scaled to smaller and smaller dimensions, the gate dielectric thickness has continued to shrink. Although further scaling of devices is still possible, scaling of the gate dielectric thickness has almost reached its practical limit with the conventional gate dielectric material, silicon dioxide. Further scaling of silicon dioxide gate dielectric thickness will involve a host of problems: extremely thin layers allow for large leakage currents due to direct tunneling through the oxide. Because such layers are formed literally from a few layers of atoms, exacting process control is required to repeatably produce such layers. Uniformity of coverage is also critical because device parameters may change dramatically based on the presence or absence of even a single monolayer of dielectric material. Finally, such thin layers form poor diffusion barriers to impurities.
Realizing the limitations of silicon dioxide, researchers have searched for alternative dielectric materials which can be formed in a thicker layer than silicon dioxide and yet still produce the same field effect performance. This performance is often expressed as xe2x80x9cequivalent oxide thicknessxe2x80x9d: although the alternative material layer may be thick, it has the equivalent effect of a much thinner layer of silicon dioxide (commonly called simply xe2x80x9coxidexe2x80x9d). In some instances, silicon dioxide has been replaced with a SiON. However, even higher-K dielectrics will soon be needed. Some films currently being investigated include deposited oxides or nitrides such as HfSiO, HfSiON, AlON, and AlZrO. Manufacturable processes for incorporating these materials are needed.